"Nicola was only 23 years old and had the whole of her life in front of her.

"We cannot express how we feel today except to say we have always been exceedingly proud of Nicola and always will be. She knew she was loved by us all and we shall all miss her dreadfully."

Ms Hughes lived in the Oldham area, and leaves behind her mother Susan, father Bryn, and younger brother Sam.

More than 2000 messages have so far been left in an online book of condolence.

Garry Shewan, Assistant Chief Constable of Greater Manchester Police, said: "Without doubt, yesterday was the hardest and most upsetting day of my career.

"The impact of yesterday's events will be felt by the force, residents of Greater Manchester and most importantly Nicola and Fiona's family, friends and colleagues for many, many years, such was the regard in which they were held."

Yesterday David Cameron led tributes to PCs Nicola Hughes and Fiona Bone.

He said that the killing was "a shocking reminder of the debt we owe to those who put themselves in danger to keep us safe and secure".

Home Secretary Theresa May said the killing of an unarmed officer attending a routine incident in Tameside, Greater Manchester, was "deeply shocking".

The murder of a woman police officer is "a terrible reminder of the risks that police officers face every day to keep our communities safe", the Home Secretary said.

Mrs May said: "This is a deeply shocking incident and a terrible reminder of the risks that police officers face every day to keep our communities safe.

"My thoughts are with the families of the officers and their colleagues at Greater Manchester Police."

The President of the Association of Police Officers Sir Hughe Orde said: "The death of two female police officers in Greater Manchester is deeply sad news for the police service.

"The two unarmed officers were responding to a routine call when faced with a dangerous and deadly situation.

"Whenever police officers and staff lose a colleague that loss is felt right across the police family. The thoughts of everyone in policing are with colleagues in Greater Manchester Police, family and friends of the two officers at this time."

"This is a painful demonstration of how police officers put themselves in harm's way every day to protect the public.

"We should pay tribute to the bravery of the two officers today who have given so much in their work to keep us safe, and our thoughts are also with their friends and colleagues in Greater Manchester Police. This is a tragedy that will be felt throughout the country."

President of the Police Superintendents' Association of England and Wales, Derek Barnett, said: "Today once again we have seen how police officers pay the ultimate price in losing their lives to protect the public.

"Whilst we still don't know the full circumstances, this tragic situation demonstrates the uniqueness of the office of constable, a duty not to walk away from danger.

"It also serves as a reminder of the risks that officers face on a regular basis.

"At the beginning of their tour of duty these two officers would have had no idea what lay ahead of them.

"I'm sure few words will offer true comfort to the families, colleagues and friends at such a difficult time, but our thoughts and prayers are with them."

Chairman of the Police Federation of England and Wales, Paul McKeever, said: "This is devastating news and our thoughts and prayers are with their families, friends and colleagues at this extremely difficult time.

"This tragedy makes us all stop and reflect on the very real dangers police officers face every day serving their local communities.

"These extremely courageous officers have sadly paid the ultimate price for their selfless actions and no words can express our regret nor comfort to their families. The entire police service throughout the UK mourn their loss.

"I know that my colleagues in Greater Manchester Police Federation will be doing everything they can to offer support and counsel to the relatives and colleagues of these brave officers."